1. Field of the Invention
This invention relates to a sabot for use with a subcaliber projectile, and more particularly, to sabots which can be used with a shotgun, with the shotgun cartridge utilized as the carrier for the sabot, projectile and propellant.
2. Description of the Prior Art
Because of the increasing technology with respect to metals, and particularly with respect to the strength imparted to metals, it is necessary to develope prdjectiles having high velocity and accuracy in order to penetrate these strengthened metals as used in present day tanks, armored vehicles and tanks. Also, more particularly, it is desirable to make weapons more versatile, e.g. utilizing a shotgun for the firing of a single projectile rather than pellets. This converts a shotgun into a longer-range weapon. With presently-marketed single projectiles, one can hit up to approximately 100 yards. With our stable and rotating projectile, one can hit at over 200 yards. Thus, the effective distance of the most common smooth-bore weapon is more than doubled by our invention.
Sabots in the past have generally been used for the purpose of adapting small caliber projectiles for firing from a larger caliber bore which effectively converts the weapon for different uses.
Ideally, it is desired to have the sabot separate from the projectile immediately upon exiting the launching tube, e.g. a rifled or smooth bore barrel, without effecting the velocity and trajectory of the projectile. Many of the prior art sabots have accomplished this to some degree. The prior art sabots relied primarily upon centrifugal forces and generated gas pressures to effect the separation of the sabot from the projectile. They also required a combination of complicated parts to make up the sabot. It can be understood that these conditions impose limitations on the efficiency of the sabot by effecting the accuracy of the projectile, by unduly restricting the type of weapon which could be used, and by creating unnecessarily high expenses to produce.
Anspacher, et al, in U.S. Pat. No. 2,998,780 discloses a sabot for a fin stabilized projectile which experiences separation upon exiting the barrel. However, closer inspection reveals that the combination of sabot and projectile is so mechanically complex that its reliability would be suspect. The greater portion of the weight of the projectile is found in the base which could cause flight instability. The fins used on the projectile are parallel with respect to the longitudinal axis of the projectile and the depth of the fins are perpendicular to the longitudinal axis which quite different from the combination contemplated by the petitioners herein. The structure utilized by Anspacher is inherently complex and expensive to fabricate. Anspacher requires a shearing action to release, which can be and usually is undependable. A principal featureof petitioners' design is a launching fin stabilized projectile from a shotgun. A projectile such as this does not require barrel riflings or the like for causing the projectile to spin.
Turning now to Manning, et al, U.S. Pat. No. 3,427,648, which teaches a sabot and finned projectile, it can be seen that the combination is a very complicated and complex structure. In normal launching of a projectile, the forward velocity increases after exiting the barrel until the gas pressure no longer acts reacts on the base of the projectile. In order to impart spin to the projectile, Manning utilizes a sabot having segments adapted to fit in the rifling grooves of the barrel such that when the weapon is fired, the sabot segments cause the projectile to follow the twist of the rifling thus inducing a stabilizing spin to the projectile. Quite unlike the petitioners' invention, Manning uses the muzzle of the gun bore for effecting the separation of the sabot and projectile. In Manning, grooves in the gun tube (barrel) are deepened causing the speed of the sabot to be retarded while in the barrel, thus permitting the projectile to exit the barrel first. One objection to this is the fact that some of the retardation would, by the inherent construction of the invention, be applied to the projectile. This would result in a less than optimum speed for the projectile, thus reducing the velocity of the projectile and denigrating the primary purpose of the sabot.
Feldman in U.S. Pat. No. 3,847,082 also discloses a spin stabilized discarding sabot projectile. Feldman also teaches a complex solution to a complex problem in that the projectile is completely encapsulated by the sabot. As a result, he must effect the separation of the projectile and sabot quite contrary to that taught by the prior art. Certain portions of the sabot rupture while being accelerated in the barrel and as the sabot clears the muzzle exit, utilizes the high pressure gases exiting the muzzle to push and disintegrate the sabot and therefore cause the separation of the sabot from the projectile. It can be seen that this type of sabot would impart its drag to the projectile. Discard of the sabot requires the segments to increase in velocity over the velocity of the subprojectile.
Bjornson, U.S. Pat. No. 4,029,018 solves the problem of sabot and projectile separation very simply. He utilizes a sabot with slotted segments at one end and unslotted portion at the other end. The unslotted portion acting as an obturator for directing the high velocity gases onto itself and the projectile. Once out of the muzzle bore, centrifugal and air forces acting on the slotted segments cause the slotted segments to disintegrate thus causing separation of the sabot and projectile. However, the sabot which is designed with internal screws is screwed on to the projectile for a supposedly tighter connection. This type of intimate connection results in any drag applied to the sabot also applied to the projectile prior to separation. There is no such connection between the sabot and projectile as contemplated by the applicant herein. Further, Bjornson does not take into account a stabilized projectile. The only concern shown is for the separation. In Bjornson, the sabot "pulls" the subprojectile during launch.
The present-day smooth bore weapon of common usage is the shotgun. Of various bore diameters and mechanical types, it has evolved from the heavy matchlock musket over the last 350 years. One can fire a cluster of small shot from it and reasonably hope to bring down a bird on the wing at 40 yards. One can fire a slug and reasonably hope to bring down a man or a deer at 100 yards. These figures have not essentially changed over the centuries. It is believed that the maximum range for single-projectile loads can reasonably be doubled at the present time.
Biology teaches us that ontogeny recapitulates phylogeny, so it should not be a matter of surprise that our thoughts here are of increasing the lethal range of firearms. In man's 5000 years of recorded history there have been about 210 years of peace. And one of his most ancient dreams has been of a weapon so powerful that all he had to do was point his finger at his adversary and blow him away.
About 1540 the Duke of Alva introduced a large heavy smooth bore matchlock into the Spanish army. It fired round lead balls, 10 to the pound, and under the name of "musket" (from the Italian "moschetto", male sparrow-hawk) came into general use throughout Europe. Ignition systems were improved over the centuries by wheelock, flintlock, percussion, and self-contained cartridge. Military small arms started evolving to their present small bore rifled configuration in the mid-nineteenth century. Smooth bore small arms have gradually evolved to the present day shotgun.
Over the centuries, the projectiles used with the smooth bore small arm have remained much the same--either a cluster of small circular shot, or one large slug which fits the bore quite snugly. A notable recent advance was the flechette (lit., little arrow), a small finned all-steel dart. These were fired individually in the "special purpose individual weapon" of the U.S. Army, and in clusters numbering into the thousands in the 105 millimeter cannon. Their penetration is however poor, being somewhat less than #5 shot (lead pellets 0.12 inch diameter). Hits and kills with any of these at ranges greater than 100 yards are problematical.
Large caliber smooth bore weapons appear in such things as tank cannons, mortars, rocket launchers, and torpedo tubes. Several of these devices depend on in-flight guidance and/or proximity fuses to secure satisfactory accuracy and maximum lethality. The scale and expense involved with these large caliber smooth bore devices make them prohibitive for the private experimenter.
Thus, unless one is prepared to work out a whole new weapons system, it is best to work with one whose limitation of range and accuracy are quite well defined: the 12 gauge shotgun. Previous attempts at loads affective at long range well known to those skilled in the art include British, French, German and American designs. All of these save the American BRI are borefitting nonrotating short fat slugs. The BRI is a discarding sabot round, 0.5 inch diameter, with what amounts to a 3 piece sabot. It has not lived up to its initial optimistic claims due to misaligned sabots and an unfavorable length/diameter ratio of the projectile itself.
Let us consider the sabot round. In a discarding sabot round, the projectile is held in a carrier and both are fired out of the cartridge case together. The carrier is made of lighter material than the projectile. Shortly after leaving the muzzle, the carrier detaches and falls away; the projectile speeds on to the target by itself. The combined weight of carrier plus small-diameter projectile is less than the weight of a bore-fitting projectile. The same amount of propellent can thus be burned under a lighter payload. In large caliber artillery pieces this has yielded markededly increased velocity and range for armor-piercing rounds. An additional benefit is that erosion of the bore by hot gases is decreased, since the gun-tube area used to attain the velocity of the projectile is greatly increased. Muzzle velocity is increased, kinetic energy of the projectile is enhanced with no change in recoil vis a vis the conventional bore-fitting projectile. Kinetic energy goes up as the square of the velocity--1/2MV.sup.2 --while the recoil remains at mv. Thus if attained breech pressures were to allow an oversimplified solution one could halve the projectile weight and double the velocity with no change in recoil but a doubling of the kinetic energy of the projectile.
The projectile and sabot must be of a structure such that the cooperation of the two individual structures enhance separation and accuracy. The shooting of a unitary projectile, ball or bullet through a barrel has a long history and a great deal of activity as evidenced by the large number of patents directed to sabots. The research, interest and activity has been directed to increasing the accuracy of the projectile as well as the kill power. In the 1860's the best that one could expect, if the ball fit the bore reasonably well, was that a man size target could be hit most of the time. Prior to this, in 1615 when the musket was introduced, the accuracy was considerably less. The applicants have solved the age old problem of effectively firing a projectile and sabot with an increase in efficiency, accuracy and velocity. Simply and elegantly by using a projectile, heavy in the forward end having fins for stabilizing and providing spin on the aft end. The fins have a 30.degree. to 40.degree. slope for lessening air resistance. The combination of a projectile with maximum diameter fins and eccentric placement on the projectile in combination with a sabot of simple construction provide a very efficient weapon system with results not accomplished in the prior art cited above.